This invention relates to an exhaust control valve system for a parallel multi-cylinder, two-cycle engine and more particularly to an improved exhaust port and control valve arrangement for such an engine that permits a compact assembly.
It is well known that the port timing in two-cycle, crankcase compression, internal combustion engines is very critical to the engine performance. It is also known that port timings that permit maximum power attainment normally provide poor running at low and mid-ranges. In a like manner, port timings that provide good low and mid-speed range running do not permit maximum power output. It has, therefore, been proposed to employ an exhaust control valve in the exhaust port that is effective to change the exhaust timing and permit optimum engine performance through a wider range of running conditions.
With most two-cycle, crankcase compression engines, there are provided a plurality of scavenge ports formed around the cylinder bore axis for transferring the compressed intake charge to the combustion chamber. Normally, there is also provided at least one exhaust port that is somewhat in confronting relationship to the intake ports. The use of such multiple ports, therefore, gives rise to a situation wherein the cylinder bore to cylinder bore spacing must be increased to provide clearance for the individual ports and passages associated with them.
One way that the engine can be made more compact is to rotate the port arrangement relative to the cylinder bore axis so as to permit the ports associated from one cylinder to nest between those of the adjacent cylinder. With inline engines, this will permit a reduction in the overall length of the engine. However, when exhaust control valves have been employed, this rotational positioning of the ports has not been done because of the difficulties in providing the control valves and operating mechanism for them.
It is, therefore, a principal object of this invention to provide an improved port and exhaust control valve arrangement for a two-cycle, crankcase compression, internal combustion engine that provides a compact assembly.
It is a further object of this invention to provide a porting and exhaust control valve arrangement for a two-cycle, crankcase compression engine that permits the ports to be rotated relative to the cylinder bore axis to achieve a compact construction while at the same time insuring ease of operation of the control valves for the exhaust ports.
It is yet another object of this invention to provide an improved exhaust port and control valve arrangement for a multiple cylinder, two-cycle, crankcase compression, internal combustion engine.